The present invention relates to a cellophaning machine wrapping and sealing method.
In particular, the present invention relates to a wrapping and sealing method for wrapping packets, particularly packets of cigarettes, in transparent material on a cellophaning machine.
On cellophaning machines, sheets of transparent material and respective packets are fed successively to a conveying device normally consisting of a roller with a number of pockets, each designed to receive a group consisting of a sheet of transparent material folded in a U, and a respective packet. The roller is turned about its axis so as to feed the groups in steps along a substantially circular path and through at least one sealing station, where, during a pause in rotation of the roller, a sealing device engages the sheet and seals it about the respective packet in the form of a tubular wrapping, the ends of which are open and project axially outwards of the respective pocket.
Once the tubular wrapping is formed, the conveying device feeds the groups successively to an unloading station, where, during respective pauses in rotation of the roller, a radial pusher, mounted in a fixed position inside the roller, expels the groups successively from the pockets on to an output conveyor. As the groups are fed forward in steps on the output conveyor, the open ends of the tubular wrappings are folded on to the ends of the packets, after which, the groups are fed between at least two opposed sealing devices, which, during a pause in the operation of the output conveyor, seal the folded opposite ends of each wrapping.
Though extremely efficient, the above known wrapping method has proved inadequate over and above a given operating speed.
Firstly, due to the presence of a reciprocating pusher for expelling the groups from the pockets on the conveying device, this must be arrested for as long as the pusher engages the unloading station. As the pusher is usually cam-activated, this obviously poses limitations on the operating speed of the pusher and, consequently, the output speed of the machine as a whole. Attempts to overcome this drawback by operating the pusher by means of a crank system have resulted in only a relatively small increase in production speed, due to the fact that, over and above a given limit, the speed of the pusher invariably damages the packets.
Secondly, over and above a given production speed, the above known wrapping method requires pairs of fixed sealing devices comprising opposed sealing plates for simultaneously sealing a number of groups. The drawback here lies in the size of the plates, which can rarely be designed so as to perfectly contact the entire end surface of the packets, thus resulting in imperfect sealing of the folded ends of the tubular wrapping. Moreover, in the event the groups are fed contacting one another between the sealing plates, the possibility also exists of the groups being sealed to one another.
Finally, further drawbacks are posed by the fact that the packets are fed forward in steps, and that the sealing devices only operate during pauses in the operation of the output conveyor. As any expert in this particular field is aware, it is extremely difficult to accurately adjust the temperature of discontinuously-operating sealing devices, in the event of a variation in the operating speed of the cellophaning machine.